Gas turbines have been used for producing power in many installations around the world. Often, the exhaust gases of the gas turbine are merely exhausted into the atmosphere. For example, high pressure natural gas transmission pipelines are conventionally used for transporting gas from production fields to customers remotely located from the fields. Gas compressors feeding such pipelines usually are powered by a gas turbine, and optionally, a heat recovery cycle can be employed to reduce the net power requirement by converting waste heat in the hot exhaust gases from the turbine into electricity. An installation of this type is illustrated schematically in FIG. 1 which shows a two stage air compressor producing compressed air that is supplied to a gas turbine coupled to a utilization device, such as a gas compressor. In such an installation, a portion of the compressed gas supplied by the compressor is bled into a combustor and burned in the compressed air before the resultant combustion gases are applied to the gas turbine.
The temperature of the hot gases that exit the gas turbine can be about 450.degree. C., and these gases usually contain sufficient heat to make heat recover economically justifiable. Conventionally, the exhaust gases are applied to an indirect contact heat exchanger containing water which is vaporized. The resultant steam is supplied to a steam turbine coupled to a generator that produces electricity, and expanded steam that exits the turbine. The expanded steam is condensed in a condenser that usually is supplied with cooling water from a pond associated with a cooling tower.
During cold weather, ambient temperature may drop below freezing causing the cooling water and the steam condensate to freeze thus interfering with the functioning of the condenser and the cooling tower. When this occurs, operation of the heat recovery cycle must be terminated.
Recent improvements in organic vapor turbine design and construction have suggested that an organic vapor turbine using an air-cooled condenser might be used to replace the steam turbine in the installation described above. This would have the advantage of permitting the heat recovery cycle to remain operational during the coldest weather. However, the high temperature of the exhaust gases and the characteristics of organic fluids (e.g., pentane) used in organic vapor turbine cycles raises the possibility that a relatively hot portion of the heat exchanger could result in carbon formation and deposition due to the excess heating of the organic fluid by the hot exhaust gases.
It is therefore an object of the present invention to provide a new and improved gas turbine system with heat recovery cycle and a method for using the same which overcomes or substantially ameliorates the problem described above.